Pittsburgh’s postwar era of Modern architecture and urban renewal lends itself to easy generalization. Shiny, diffident corporate boxes punctuate neighborhood-killing mega-projects in a relentless concrete landscape, precious few of whose irreversible changes materialized as actual improvements. Yet, Imagining the Modern, over,under’s ambitious exhibition of architecture in that place and period, aims for a more multivalent presentation.

The innocence, or naiveté, of the immediate postwar era is present here, sprouting in little-known publications such as Mitchell & Ritchey’s Pittsburgh in Progress of 1947. Commissioned by retail magnate and Fallingwater patron Edgar Kaufmann, the pamphlet foresees a more vast clean-slate redevelopment of Pittsburgh than ever actually came to pass. Intended as an enticement, it seems cautionary now.

It is also emblematic of the rich selection of period materials — newspapers, professional journals, and pamphlets — some under glass, some reproduced, and others open for perusing. These portray urban renewal as a much more episodic, contentious, and changeable entity than its current inevitability would indicate. Underscoring that sense, the curators meticulously document, in palimpsest- like site plans, the unrealized projects that were planned on the sites where constructions came to pass. These documents will delight specialists but perhaps befuddle novices.

Amid the Heinz’s Postmodern galleries, the curators use one large space as a real studio — Carnegie Mellon architecture students are at work on redesigns of the fortress-like Allegheny Center Mall of 1966 for course credit. They ambitiously repurpose an active gallery space, and the end results, even with preliminary sketches and models hanging up, are unknown. But the approach reflects an open and responsive attitude toward architectural process and the accompanying exhibit that Modern architecture itself had in small though insufficient amounts.